A new report by Internet experts says the network held up well under the strain of last year's terrorist attacks against New York's World Trade Center, even though the building's collapse crushed communications equipment and networks. But the experts suggest that certain steps should be taken to ensure that another disaster avoids greater disruption.

From its beginnings as a U.S. military research network in the 1960s, the Internet has been highly decentralized with unique ways of ensuring that data reach their destination.

While telephone networks limit the volume of calls, the Internet allows increasing data volume but at a slower rate, like a highway clogged with cars.

The rationale behind the design was to keep the system working even if a natural disaster or malicious attack caused individual components to fail.

A report from the U.S. National Academy of Sciences says this design helped the Internet to sniff out damage and route around after last year's terrorist attacks in the United States.

The chairman of the panel that wrote the report is Craig Partridge, the chief scientist at the East Lansing, Michigan, company BBN Technologies. "If you look at the Internet as a whole, September 11 was not a big deal," he says. "That is to say, we didn't lose a lot of connectivity. We saw a lot of flexibility to route around any problems that occurred."

The panel found that serious effects to the Internet were isolated to a few locations. "Just because September 11 as a whole wasn't a big deal on the Internet doesn't mean that on certain parts of the Internet you weren't having a very bad day," says Mr. Partridge. "Indeed, certain parts of the world did have a bad day. New York was one and even more striking, places like South Africa and parts of Eastern Europe were others."

That is because New York operates as a communications super-hub for several countries that find it cheaper to lease connection links in New York than run land lines across borders.

The report finds that most of the damage was quickly remedied through improvisation, rapid deployment of new equipment, and rerouting of Internet traffic to bypass failed parts.

The panel says the September 11 experience does not necessarily indicate how the Internet would fare if attacked directly. But committee member Sean Donelan, head of Internet Security at SBC Communications in Sunnyvale, California, says such an attack would not doom the entire system. "There isn't really any single point of failure that we could identify," he says. "Destroying a few Internet connection points would probably not bring down the Internet. There is just too much rich interconnectivity between various providers, carriers, and so forth in the New York City area."

Still, the panel notes that businesses and services that rely on the Internet should review their dependency and plan accordingly. For example, doctors at a New York City hospital could not use their wireless handheld computers on September 11 to gain access to medical information.

The attacks also heavily damaged the Internet infrastructure of the New York Stock Exchange and member firms, and a surge in demand for information overwhelmed the Internet capacity of at least two major news services.

National Academy of Sciences panel member David Clark of the Massachusetts Institute of Technology says such operations should ensure adequate communications backup. He says what helped many New York financial institutions on September 11 is the redundancy they installed after the 1993 bombing of the World Trade Center. They woke up and said, 'okay, we have to replicate our resources and we have to make sure it actually works,' and they did tests. So even firms where damage to their infrastructure in the World Trade Center was total and the loss of life was catastrophic, their systems kept running," he says.

The National Academy committee noted that the vulnerability of the power grid affects the Internet. So does that of the telephone system because Internet service providers coordinate by phone in emergencies. As a result, the panels says disaster plans, more coordination with local authorities, and a means of restoring service remotely are needed to deal with power failures and telephone outages.